Thermally expanded microspheres and a process for producing the same

ABSTRACT

The present invention provides heat-expanded microspheres having high packing efficiency, and a production method thereof. The heat-expanded microspheres are produced by expanding heat-expandable microspheres, which comprise shell of thermoplastic resin and a blowing agent encapsulated therein having a boiling point not higher than the softening point of the thermoplastic resin and have an average particle size from 1 to 100 micrometer, at a temperature not lower than their expansion initiating temperature, and the heat-expanded microspheres result in a void fraction not higher than 0.70.

TECHNICAL FIELD

The present invention relates to heat-expanded microspheres, and aproduction process thereof.

TECHNICAL BACKGROUND

Heat-expandable microspheres which have a structure comprising a shellof thermoplastic resin and a blowing agent encapsulated therein aregenerally called heat-expandable microcapsules. Thermoplastic resinsusually include vinylidene chloride copolymers, acrylonitrilecopolymers, and acrylic copolymers, and blowing agents mostly employedare hydrocarbons, such as isobutane and isopentane. (Refer to PatentReference 1.)

Such heat-expandable microcapsules are processed into lightweight hollowparticulates (heat-expanded microspheres) by heating and expanding. Forexample, a process of spraying a dispersion of heat-expandablemicrocapsules into hot air to simultaneously expand and dry themicrocapsules has been proposed as a process for expandingheat-expandable microcapsules. (Refer to Patent Reference 2.) Theprocess, however, presents a problem, in that the deposition ofaggregated microcapsules at the end of the spray used is highly likely.

For solving those problems described above, the inventors of the presentinvention have developed a process for producing hollow particulateswherein heat-expandable microcapsules are heated and expanded in dry hotgas flow, the residual amount of unexpanded raw material, i.e. theheat-expandable microcapsule, in the expanded microcapsule is lowered,and the generation of aggregated microspheres is minimized. (Refer toPatent Reference 3.)

[Patent Reference 1] U.S. Pat. No. 3,615,972

[Patent Reference 2] JP B 59-53290

[Patent Reference 3] WO 2005/049698

DISCLOSURE OF INVENTION Technical Problem

Although the property of heat-expanded microspheres produced in theprocess is rather satisfactory, further improvement in their property isrequired. For example, hollow microspheres are exceedingly bulky fortheir weight in most cases (in other words, they have low packingefficiency and high void fractions). Thus they cause problems, such asextremely poor storing efficiency and transferring efficiency.

When heat-expanded microspheres are mixed with other materials to bemade into hollow particulate composition, the heat-expanded microspheresmay be destroyed or collapsed by external force (mixing stress) in themixing and agitating operation. For this reason, heat-expandedmicrospheres are required to be highly resistant to mixing stress (or tohave repeated-compression durability). When heat-expandable microspheresare heated excessively, they form aggregated microspheres (excessivelyexpanded microspheres), which have comparatively thin shell for theirdiameter. The thin shell of excessively expanded microspheres leads to aproblem, that is, poor durability of the microspheres against repeatedcompression.

The object of the present invention is to provide heat-expandedmicrospheres having high packing efficiency and to provide a productionprocess thereof.

Technical Solution

For solving the problems described above, the inventors of the presentinvention have studied diligently and drawn out a conclusion that thepacking efficiency of hollow microspheres is improved by increasing thenumber of hollow microspheres filled in a certain volume, and that theshortest way to the improvement is to improve the method of producinghollow microspheres in dry process which had been developed by theinventors as disclosed in the Patent Reference 3. In the course of studyfor the improvement of the production process, the inventors have founda problem caused by the heating apparatus, that is, inconstanttemperature of the hot gas flow, which sometimes fluctuates in a widerange about 50 degree.C. depending on the points of temperaturemeasurement (i.e., temperature variation depending on the measuringpoints in hot gas flow). Then the inventors have newly found thatminimizing the variation of hot gas temperature with some design ormodification enables the production of heat-expanded microspheres havinghigh packing efficiency (in other words, low void fractions) and highdurability to repeated compression, and have achieved the presentinvention.

The heat-expanded microspheres of the present invention are produced ina method in which heat-expandable microspheres, each of which comprisesa shell of thermoplastic resin and a blowing agent encapsulated thereinhaving a boiling point not higher than the softening point of thethermoplastic resin and has an average particle size ranging from 1 to100 micrometer, are heated to a temperature not lower than theirexpansion initiating temperature and expanded. The void fraction of theheat-expanded microspheres is 0.70 or less.

The method of producing the heat-expanded microspheres of the presentinvention comprises the steps of feeding a gas fluid containing aplurality of heat-expandable microspheres, each of which comprises ashell of thermoplastic resin and a blowing agent encapsulated thereinhaving a boiling point not higher than the softening point of thethermoplastic resin, and has an average particle size ranging from 1 to100 micrometer, through a gas-introducing tube equipped with adispersion nozzle on its outlet and fixed inside a hot gas flow, andthen jetting the gas fluid from the dispersion nozzle; making the gasfluid collide with a collision plate fixed under the dispersion nozzlein order to disperse the heat-expandable microspheres in the hot gasflow; and bringing the dispersed heat-expandable microspheres intocontact with the hot gas flow, the temperature difference of which doesnot exceed 40 degree.C., and heating them at a temperature not lowerthan the expansion initiating temperature of the heat-expandablemicrospheres and thus expanding the same.

Another method of producing the heat-expanded microspheres of thepresent invention comprises the steps of; feeding a gas fluid containinga plurality of heat-expandable microspheres, each heat-expandablemicrosphere comprising a shell of thermoplastic resin and a blowingagent encapsulated therein having a boiling point not higher than thesoftening point of the thermoplastic resin, and the plurality ofheat-expandable microspheres having an average particle size from 1 to100 micrometer, through a gas-introducing tube equipped with adispersion nozzle on an outlet thereof and fixed inside a hot gas flow,and then jetting the gas fluid from the dispersion nozzle; making thegas fluid collide with a collision plate fixed on a downstream positionof the dispersion nozzle in order to disperse the heat-expandablemicrospheres in the hot gas flow; and heating the dispersedheat-expandable microspheres in the hot gas flow, which containsturbulent flow generated by a turbulent flow generating member set at anupstream position of the hot gas flow, at a temperature not lower thanthe expansion initiating temperature of the heat-expandable microspheresand thus expanding the same.

ADVANTAGEOUS EFFECTS

The heat-expanded microspheres of the present invention have highpacking efficiency. In addition, the heat-expanded microspheres of thepresent invention contain extremely low amount of aggregatedmicrospheres or microspheres of high true specific gravity, and haveexcellent flowability and minimum variation in their mass specificgravity.

In a method of producing the heat-expanded microspheres of the presentinvention, dispersed heat-expandable microspheres are contacted to thehot gas flow the temperature of which varies in a range within 40degree.C. and/or which contains turbulent flow generated with aturbulent flow generating member set at an upstream position of the hotgas flow, and thus the heat-expandable microspheres are heated andexpanded at almost constant temperature. Consequently the resultantheat-expanded microspheres have high packing efficiency. In addition,the resultant heat-expanded microspheres contain extremely low amount ofaggregated microspheres generated from excessive heating (excessivelyexpanded microspheres) or microspheres of high true specific gravitygenerated from insufficient heating, have minimum variation in theirmass specific gravity, and are excellent in their flowability andrepeated-compression durability.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 (a) a diagram of the expanding device of the manufacturingequipment, and (b) a plan view illustrating temperature levels at acertain plane in hot gas flow.

FIG. 2 A diagram of an example of the expanding device of themanufacturing equipment employed in a production process of the presentinvention.

FIG. 3 A diagram of another example of the expanding device of themanufacturing equipment employed in a production process of the presentinvention.

FIG. 4 A diagram of yet another example of the expanding device of themanufacturing equipment employed in a production process of the presentinvention.

EXPLANATION OF REFERENCES

-   -   1: Hot gas nozzle    -   2: Cooling medium flow    -   3: Overheating preventive tube    -   4: Dispersion nozzle    -   5: Collision plate    -   6: Gas fluid containing heat-expandable microspheres    -   7: Inert gas flow    -   8: Hot gas flow    -   9: Mesh    -   10: Ring    -   11: Expansion chamber

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is described in detail below.

[Heat-Expandable Microspheres]

The heat-expandable microspheres used in the production process of thepresent invention have an average particle size ranging from 1 to 100micrometer, and comprise a shell of thermoplastic resin and a blowingagent which has a boiling point not higher than the softening point ofthe thermoplastic resin and is encapsulated in the shell; and each ofthe heat-expandable microspheres exhibits heat-expandability as a whole(or expands under heating as a whole).

The blowing agent is not specifically restricted so far as it is asubstance having a boiling point not higher than the softening point ofthe thermoplastic resin. The examples of such blowing agents are C₁₋₁₂hydrocarbons and their halogen compounds, fluorine compounds, tetraalkylsilane, and compounds which thermally decompose to generate gas, such asazodicarbonamide. One of those blowing agents or a mixture of at leasttwo of them may be employed.

The examples of the C₁₋₁₂ hydrocarbons are propane, cyclopropane,propylene, butane, normal butane, isobutane, cyclobutane, normalpentane, cyclopentane, isopentane, neopentane, normal hexane, isohexane,cyclohexane, heptane, cycloheptane, octane, isooctane, cyclooctane,2-methyl pentane, 2,2-dimethyl butane, and petroleum ether. Any of thesehydrocarbons having a linear, branched or ali-cyclic structure areemployable, and aliphatic hydrocarbons are preferable.

The examples of the halogen compounds of C₁₋₁₂ hydrocarbons are methylchloride, methylene chloride, chloroform, and carbon tetrachloride.Above all halogen compounds (fluorine compounds, chlorine compounds,bromine compounds, iodine compounds, etc.) of the above-mentionedhydrocarbons are preferable.

The fluorine compounds are not specifically restricted so far as theycontain fluorine atoms in their molecules, and C₂₋₁₀ compounds having anether structure and containing no chlorine and bromine compounds arepreferable. Examples of such fluorine compounds are hydrofluoroethers,such as C₃H₂F₇OCF₂H, C₃HF₆OCH₃, C₂HF₄OC₂H₂F₃, C₂H₂F₃OC₂H₂F₃, C₄HF₈OCH₃,C₃H₂F₅OC₂H₃F₂, C₃HF₆OC₂H₂F₃, C₃H₃F₄OCHF₂, C₃HF₆OC₃H₂F₅, C₄H₃F₆OCHF₂,C₃H₃F₄OC₂HF₄, C₃HF₆OC₃H₃F₄, C₃F₇OCH₃, C₄F₉OCH₃, C₄F₉OC₂H₅, andC₇F₁₅OC₂H₅. Those hydrofluoroethers may have either linear or branched(fluoro) alkyl groups.

Any of blowing agents having a boiling point not higher than thesoftening point of the thermoplastic resin may be employed. The blowingagent may wholly comprise fluorine compounds, and may comprise themixture of fluorine compounds and compounds other than fluorinecompounds having a boiling point not higher than the softening point ofthe thermoplastic resin. Such compounds are not specifically restricted,and those selected from the examples of blowing agents described abovecan be used. Compounds other than fluorine compounds may appropriatelybe selected according to the range of the expanding temperature ofheat-expandable microspheres.

In a blowing agent containing a fluorine compound, the weight ratio ofthe fluorine compound is preferably greater than 50 weight percent ofthe whole of the blowing agent, more preferably greater than 80 weightpercent, and most preferably greater than 95 weight percent. Greaterweight ratio of a fluorine compound in a blowing agent gives moreinfluence of the properties of the fluorine compound to heat-expandablemicrospheres so as to impart flame retarding and flameproof propertiesto the heat-expandable microspheres.

The heat-expandable microspheres comprise a thermoplastic resin, forexample, a resin produced by polymerizing a monomer mixture consistingessentially of a radically polymerizable monomer. The monomer mixture isblended with a proper amount of a polymerization initiator to bepolymerized and formed into the shell of the heat-expandablemicrospheres.

The radically polymerizable monomers, which are not specificallyrestricted, include nitrile monomers, such as acrylonitrile,methacrylonitrile, alpha-chloracrylonitrile, alpha-ethoxyacrylonitrile,and fumaronitrile; monomers having carboxyl groups, such as acrylicacid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, andcitraconic acid; vinylidene chloride; vinyl acetate; (meth)acrylatemonomers, such as methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl(meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate,isobornyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl(meth)acrylate, and beta-carboxyethyl acrylate; styrene monomers, suchas styrene, alpha-methyl styrene, and chlorostyrene; acryl amidemonomers, such as acryl amide, substituted acryl amide, methacrylicamide, and substituted methacrylic amide; and maleimide monomers, suchas N-phenyl maleimide, N-(2-chlorophenyl) maleimide, N-cyclohexylmaleimide, and N-lauryl maleimide. All or part of the carboxyl groups inthe monomers having carboxyl groups may be neutralized inpolymerization.

One of or a mixture of at least two of those radically polymerizablemonomers may be used. Above all a monomer mixture containing at leastone radical polymerizable monomer selected from the group consisting ofnitrile monomers, (meth)acrylate monomers, monomers having carboxylgroups, styrene monomers, vinyl acetate, and vinylidene chloride ispreferable. In particular, a monomer mixture consisting essentially of anitrile monomer is preferable. The preferable weight ratio of thenitrile monomer in the monomer mixture is at least 20 weight percent,more preferably at least 50 weight percent, and most preferably at least70 weight percent. For achieving satisfactory heat resistance of theshell of microspheres, the preferable weight ratio of the nitrilemonomer is at least 80 weight percent, more preferably at least 90weight percent, and most preferably at least 95 weight percent.

A monomer mixture containing a nitrile monomer and a monomer having acarboxyl group is more preferable, because such monomer mixture impartsheat resistance to heat-expandable microspheres, imparts re-expandingcapacity to heat-expanded microspheres produced by expanding theheat-expandable microspheres, and simultaneously enables theheat-expanded microspheres to start re-expansion at 90 degree.C. orhigher temperature (preferably at 100 degree.C. or higher and morepreferably at 120 degree.C. or higher). The weight ratio of the nitrilemonomer in the monomer mixture should preferably range from 20 to 80weight percent, more preferably from 20 to 60 weight percent, furtherpreferably from 20 to 50 weight percent, and most preferably from 20 to40 weight percent, for controlling the retention and blowing performanceof a blowing agent encapsulated in microspheres and the re-expansioninitiating temperature of heat-expanded microspheres. The weight ratioof the monomer having carboxyl groups in the monomer mixture shouldpreferably range from 20 to 80 weight percent, more preferably from 40to 80 weight percent, further preferably from 50 to 80 weight percent,and most preferably from 60 to 80 weight percent, for controlling there-expansion initiating temperature of heat-expanded microspheres andthe retention and blowing performance of a blowing agent encapsulated inmicrospheres.

In addition to the radically polymerizable monomers mentioned above, themonomer mixture may contain a polymerizable monomer (a cross-linkingagent) having at least two polymerizable double bonds. Thepolymerization with a cross-linking agent leads to decreased ratio ofaggregated microspheres in heat-expanded microspheres produced by theproduction process of the present invention, and minimized loss in theretention of encapsulated blowing agent in heat-expanded microspheres,which is effective to thermally expand microspheres.

In the present invention, the retention (percent) of an encapsulatedblowing agent in heat-expanded microspheres is defined as G₂/G₁×100,where G₁ is the ratio of a blowing agent encapsulated in heat-expandablemicrospheres before expansion, and G₂ is the ratio of the blowing agentencapsulated in heat-expanded microspheres produced by heating andexpanding the heat-expandable microspheres.

The cross-linking agent is not specifically restricted, and includesaromatic divinyl compounds, such as divinyl benzene and divinylnaphthalene; and di(meth)acrylates, such as allyl methacrylate,triacrylformal, triallyl isocyanate, ethylene glycol di(meth)acrylate,diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate,1,4-butanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate,1,10-decanediol di(meth)acrylate, PEG (200) di(meth)acrylate, PEG (400)di(meth)acrylate, PEG (600) di(meth)acrylate, neopentylglycoldi(meth)acrylate, 1,4-butanediol dimethacrylate, 1,6-hexanedioldi(meth)acrylate, 1,9-nonanediol di(meth)acrylate, trimethylolpropanetrimethacrylate, glycerin dimethacrylate, dimethylol tricyclodecanediacrylate, pentaerythritol tri(meth)acrylate, pentaerythritoltetraacrylate, dipentaerythritol hexaacrylate, neopentylglycol acrylicacid benzoate, trimethylolpropane acrylic acid benzoate,2-hydroxy-3-acryloyloxypropyl methacrylate, hydroxypivalic acidneopentylglycol diacrylate, ditrimethylolpropane tetraacrylate, and2-butyl-2-ethyl-1,3-propanediol diacrylate. One of or a mixture of atleast two of those cross-linking agents are applicable.

In the above description, the series of the compounds written as “PEG(#***) dimethacrylate” are polyethylene glycol di (meth)acrylate,wherein the average molecular weight of their polyethylene glycolmoieties is represented by the number in the parentheses.

The weight ratio of the cross-linking agents is not particularlyrestricted, and the preferable weight ratio ranges from 0.01 to 5 weightpercent of the monomer mixture, more preferably from 0.05 to 3 weightpercent, considering the degree of cross-linking, the retention of ablowing agent encapsulated in the shell of microspheres, and the heatresistance and heat-expanding performance of the microspheres.

The polymerization initiator is not specifically restricted, and knownpolymerization initiators may be used. The examples of thosepolymerization initiators are peroxides, such as t-butylperoxyisobutylate, t-butyl peroxy-2-ethylhexanoate, t-hexylperoxy-2-ethylhexanoate, 2,5-dimethyl-2,5-bis(2-ethylhexanoylperoxy)hexane, 1,1,3,3-tetramethylbutyl peroxy-2-ethylhexanoate, t-butylperoxypivalate, t-hexyl peroxypivalate, t-butyl peroxyneodecanoate,t-hexyl peroxyneodecanoate, 1-cyclohexyl-1-methylethylperoxyneodecanoate, 1,1,3,3-tetramethylbutyl peroxyneodecanoate, cumylperoxyneodecanoate, t-butyl peroxy-3,5,5-trimethylhexanoate, octanoylperoxide, lauroyl peroxide, stearyl peroxide, succinic acid peroxide,and benzoil peroxide; and azo compounds, such as 2,2′-azobis(4-methoxy-2,4-dimethyl valeronitrile), 2,2′-azobis isobutyronitrile,2,2′-azobis (2,4-dimethyl valeronitrile), 2,2′-azobis (2-methylpropionate), and 2,2′-azobis (2-methyl butyronitrile). Preferablepolymerization initiators are oil-soluble polymerization initiatorswhich are soluble in radically polymerizable monomers.

The weight ratio of the polymerization initiators is not particularlyrestricted, and the preferable weight ratio ranges from 0.2 to 7.0weight percent of the monomer mixture, more preferably from 0.3 to 5.0weight percent, and most preferably from 0.4 to 3.0 weight percent,considering the expanding performance of microspheres and the retentionof a blowing agent encapsulated in the microspheres.

The heat-expandable microspheres are produced with the techniquesemployed in known methods of producing heat-expandable microcapsules. Inan example of the methods of producing heat-expandable microspheres, amonomer mixture consisting essentially of a radical polymerizablemonomer and optionally containing a cross-linking agent is mixed with ablowing agent and a polymerization initiator, and the resultant mixtureis suspension-polymerized in an aqueous suspension containing a propersuspension stabilizer.

The examples of the dispersion stabilizers in the aqueous suspension arecolloidal silica, colloidal calcium carbonate, magnesium hydroxide,calcium phosphate, aluminum hydroxide, ferric hydroxide, calciumsulfate, sodium sulfate, calcium oxalate, calcium carbonate, bariumcarbonate, magnesium carbonate, and alumina sol. The preferable ratio ofthe dispersion stabilizer in the monomer mixture ranges 0.1 to 20 weightpercent. In addition, dispersion-stabilizing auxiliaries exemplified bypolymer-type dispersion-stabilizing auxiliaries including diethanolamine-aliphatic dicarboxylic acid condensates, gelatine, polyvinylpyrolidone, methyl cellulose, polyethylene oxide, and polyvinyl alcohol;and emulsifiers including cationic surfactants such as alkyltrimethylammonium chloride and dialkyldimethyl ammonium chloride, anionicsurfactants such as sodium alkyl sulfate, and amphoteric surfactantssuch as alkyldimethyl betaine aminoacetate and alkyldihydroxyethylbetaine aminoacetate may be employed. The preferable ratio of thedispersion-stabilizing auxiliaries ranges from 0.05 to 2 weight percentof the monomer mixture.

An aqueous suspension containing a dispersion stabilizer is prepared bymixing a dispersion stabilizer and dispersion stabilizing auxiliary inwater (for example, deionized water). The pH of the aqueous suspensionin polymerization is properly determined according to the variants of adispersion stabilizer and dispersion stabilizing auxiliary. Awater-soluble reducing agent may be added to the aqueous suspension, andit restrains the generation of aggregated microspheres duringpolymerization. The examples of the water-soluble reducing agents arenitrites of alkali metals, such as sodium nitrite and potassium nitrite,stannous chloride, stannic chloride, ferrous chloride, ferric chloride,ferrous sulfate, and water-soluble ascorbic acids. Above all nitrites ofalkali metals are preferable for their stability in water. Thepreferable ratio of the reducing agents ranges from 0.0001 to 1 weightpercent of the monomer mixture, more preferably from 0.0003 to 0.1weight percent.

The polymerization temperature is controlled according to the variantsof polymerization initiators, and it should preferably range from 40 to100 degree.C., more preferably from 45 to 90 degree.C., and mostpreferably from 50 to 85 degree.C. The initial pressure for thepolymerization should preferably range from 0 to 5.0 MPa in gagepressure, more preferably from 0.1 to 3.0 MPa, and most preferably from0.2 to 2.0 MPa.

The ratio of the blowing agent in the resultant heat-expandablemicrospheres should preferably be controlled within the range from 2 to85 weight percent of the microspheres, more preferably from 5 to 60weight percent, and most preferably from 7 to 50 weight percent, fromthe view point of attaining excellent blowing performance of theheat-expandable microspheres and controlling the thickness of thethermoplastic resin shell of the heat-expandable microspheres in orderto maintain a proper retention of encapsulated blowing agent. Thepreferable ratio of a blowing agent containing fluorine compounds rangesfrom 10 to 60 weight percent, more preferably from 15 to 50 weightpercent.

The average particle size of the heat-expandable microspheres may befreely designed according to their application, and therefore is notspecifically limited. A normal average particle size ranges from 1 to100 micrometer, preferably from 2 to 80 micrometer, and more preferablyfrom 5 to 60 micrometer.

The coefficient of variation, CV, of the particle size distribution ofthe heat-expandable microspheres is not particularly restricted, and itis preferably 30 percent or less, more preferably 27 percent or less,and most preferably 25 percent or less. The coefficient of variation,CV, is calculated by the following expressions (1) and (2):

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 1} \right\rbrack & \; \\{{C\; V} = {\left( {{s/} < x >} \right) \times 100\mspace{14mu} ({percent})}} & (1) \\{s = \left\{ {\sum\limits_{i = 1}^{n}\; {\left( {{{xi} -} < x >} \right)^{2}/\left( {n - 1} \right)}} \right\}^{1/2}} & (2)\end{matrix}$

where s is a standard deviation of particle size, <x> is an averageparticle size, xi is a particle size of an i-th particulate, and n isthe number of particulates.

Some components other than the shell material or blowing agent may beadded to or used to modify heat-expandable microspheres. For example,adhering a particulate filler on the outer surface of the shell ofheat-expandable microspheres is preferable for improving theirdispersibility and flowability in use.

The particulate filler may be either of an organic and inorganicfillers, and the variants and amount of particulate fillers are selectedaccording to the use of microspheres.

The examples of organic fillers are metal soaps, such as magnesiumstearate, calcium stearate, zinc stearate, barium stearate, and lithiumstearate; synthetic waxes, such as polyethylene wax, lauric acid amide,myristic acid amide, palmitic acid amide, stearic acid amide, andhydrogenated castor oil; and resin powders, such as polyacrylamide,polyimide, nylon, methyl polymethacrylate, polyethylene, andpolytetrafluoroethylene.

The examples of inorganic fillers are those having a layered structure,such as talc, mica, bentonite, sericite, carbon black, molybdenumdisulfide, tungsten disulfide, carbon fluoride, calcium fluoride, andboron nitride; and others, such as silica, alumina, isinglass, calciumcarbonate, calcium hydroxide, calcium phosphate, magnesium hydroxide,magnesium phosphate, barium sulfate, titanium dioxide, zinc oxide,ceramic beads, glass beads, and crystal beads.

One of or a mixture of at least two of the particulate fillers may beemployed.

The average particle size of the particulate fillers is preferably notgreater than one tenth of the average particle size of heat-expandablemicrospheres before adhering the particulate filler. The averageparticle size means the average particle size of primary particles.

The amount of a particulate filler adhered onto the heat-expandablemicrospheres is not specifically limited, and should preferably rangefrom 0.1 to 95 weight percent of heat-expandable microspheres beforeadhering the filler, more preferably from 0.5 to 60 weight percent,further preferably from 5 to 50 weight percent, and most preferably from8 to 30 weight percent, for properly controlling the true specificgravity of heat-expandable microspheres and optimizing the function of aparticulate filler.

A particulate filler is adhered onto the outer surface ofheat-expandable microspheres by mixing heat-expandable microspheres anda particulate filler. The mixing process is not specifically restricted,and a device of a very simple mechanism, such as a vessel and paddleblades, is employable. Ordinary powder mixers for shaking or agitatingpowders are also applicable. The powder mixers include those which canshake and agitate, or agitate powders, such as ribbon-type mixers andvertical screw mixers. Recently, highly efficient multi-functionalpowder mixers manufactured by combining several agitation devices, suchas Super Mixer (manufactured by Kawata MFG Co., Ltd.), High-Speed Mixer(manufactured by Fukae Co., Ltd.) and New-Gram Machine (manufactured bySeishin Enterprise Co., Ltd.), have become available.

The moisture content of the heat-expandable microspheres shouldpreferably be 5 weight percent or less, more preferably 3 weight percentor less, for uniform heating and expanding.

The heat-expandable microspheres are applicable as a lightweight fillerfor automobile paints, expanding particles in expandable inks forwallpaper and apparel design, an expanding material for lightening resincompositions, a sensitizer for explosives, a light diffuser, and avoid-forming agent.

[Production Process for Heat-Expanded Microspheres]

The production method of the heat-expanded microspheres of the presentinvention comprises the steps of feeding a gas fluid containingheat-expandable microspheres, the starting material described above,through a gas-introducing tube equipped with a dispersion nozzle on itsoutlet and fixed inside a hot gas flow, and then jetting the gas flowfrom the dispersion nozzle (jetting step); making the gas fluid collideon a collision plate fixed under the dispersion nozzle to disperseheat-expandable microspheres into the hot gas flow (dispersing step);and heating the dispersed heat-expandable microspheres in the hot gasflow at a temperature not lower than their expansion initiatingtemperature, where the difference in the heating temperature is notgreater than 40 degree.C., so as to expand the heat-expandablemicrospheres (expanding step).

Another production method of the heat-expanded microspheres of thepresent invention comprises the steps of feeding a gas fluid containingheat-expandable microspheres, the starting material described above,through a gas-introducing tube equipped with a dispersion nozzle on itsoutlet and fixed inside a hot gas flow, and then jetting the gas flowfrom the dispersion nozzle (jetting step); making the gas fluid collideon a collision plate fixed under the dispersion nozzle to disperseheat-expandable microspheres into the hot gas flow (dispersing step);and heating the dispersed heat-expandable microspheres in the hot gasflow, which contains turbulent flow generated by a turbulent flowgenerating member set at an upstream position of the hot gas flow, at atemperature not lower than their expansion initiating temperature so asto expand the heat-expandable microspheres (expanding step).

In the two production methods mentioned above, the same jetting anddispersing steps are employed. One of the expanding steps may furtherinclude the conditions of another expanding step.

The expanding device of the manufacturing equipment used in theproduction method of the present invention is explained referring toFIG. 1 (a), which shows the structure common to all of such equipment.The expanding device in FIG. 1 (a) is mere an example of such device,and the expanding device is not restricted within its category. Theexpanding device comprises a gas introducing tube (without a referencenumeral) equipped with a dispersion nozzle 4 on its outlet and fixed atthe center of the equipment, a collision plate 5 set under thedispersion nozzle 4, an overheating preventive tube 3 fixed around thegas introducing tube with some distance, and a hot gas nozzle 1 fixedaround the overheating preventive tube with some distance. At theexpanding device, a gas fluid 6 containing heat-expandable microspheresis flowed through the gas introducing tube in the direction marked withthe arrow, and an inert gas 7 is flowed through the space between thegas introducing tube and the overheating preventive tube 3 in thedirection marked with the arrow in order to improve the dispersion ofheat-expandable microspheres and to prevent the overheating of the gasintroducing tube and collision plate. In addition, hot gas flow 8 issupplied in the direction marked with the arrow in the space between theoverheating preventive tube 3 and the hot gas nozzle 1. In theoverheating preventive tube 3, a cooling medium flow 2 is flowed forcooling in the direction marked with the arrow. Overheating-preventivefunction should preferably be imparted to the gas introducing tubeand/or the collision plate 5 for minimizing aggregated or fusedmicrospheres.

The collision plate 5 may be fixed on a part, such as thegas-introducing tube mentioned above, and may be fixed on a part otherthan the parts mentioned above. The shape of the collision plate 5 isnot specifically restricted, and the examples of the form includefusiform, conical, pyramid, spherical, hemispherical, or a combinationthereof.

At the jetting step, the gas fluid 6 containing heat-expandablemicrospheres is flowed through the gas introducing tube equipped withthe dispersion nozzle 4 on its outlet and fixed at the inside of the hotgas flow 8, and the gas fluid 6 is jetted from the dispersion nozzle 4.The gas fluid 6 is not specifically restricted and may be any of gasescontaining heat-expandable microspheres. An inert gas such as air,nitrogen, argon, and helium containing heat-expandable microspheres ispreferable. The moisture content of the gas fluid 6 is preferably notgreater than 30 g/m³, and more preferably not greater than 9.3 g/m³, fordispersing heat-expandable microspheres. The flow rate of the gas fluid6 is not specifically restricted, but it should be controlled at a ratewhich enables each of heat-expandable microspheres to be subjected tothe same thermal history so far as possible and be expanded in the hotgas flow 8 at the subsequent dispersing step.

Then at the dispersing step, the gas fluid 6 collides to the collisionplate 5 fixed under the dispersion nozzle 4 so as to disperse theheat-expandable microspheres uniformly in the hot gas flow 8. The gasfluid 6 emitted from the dispersion nozzle 4 is introduced to thecollision plate 5 with the inert gas flow 7, and collide to the plate.

Finally at the expanding step, the dispersed heat-expandablemicrospheres are heated and expanded in the hot gas flow 8 at atemperature not lower than the expansion initiating temperature of themicrospheres. The hot gas flow for the heating has a temperaturedifference within 40 degree.C. and/or contains turbulent flow generatedwith a turbulent flow generating member fixed at an upstream position ofthe hot gas flow. This enables almost all of heat-expandablemicrospheres to be subjected to almost the same thermal historycontinuously, and the resultant heat-expanded microspheres have highpacking efficiency.

Various ideas were contributed for producing heat-expanded microsphereshaving high packing efficiency. Supplying hot gas, which has alreadybeen heated to a certain temperature, to heat-expandable microspheres isan example of such ideas. Only with the idea, however, hot gas flow ofconstant temperature may not be supplied uniformly (with constant flowrate or pressure) and continuously to be contacted to heat-expandablemicrospheres, because various factors, such as the diameter andcurvature of hot gas flow supplying pipe of the manufacturing equipment,flow rate of hot gas flow, and the diameter of each nozzle, relatecomplicatedly to the hot gas supply. For example, the hot gas flowsupplying pipe is usually short and has curved structure for minimizingthermal loss. At the outer side of the curved part, the temperature ofhot gas is measured higher while the temperature of the hot gas at theinner side of the curved part is measured lower. In such cases,resultant heat-expanded microspheres have low void fraction that is morefrequent than expected. However, the above-mentioned simple technique,which subjects all of heat-expandable microspheres to hot gas havingminimum range of temperature distribution, enables production ofheat-expanded microspheres having excellent packing efficiency.

The phrase “temperature difference within 40 degree.C. in gas flow”means that the difference between the maximum and minimum temperatures(hereinafter sometimes referred to only as “temperature difference”)detected at several points in the hot gas flow 8 just before or at thecontact with dispersed heat-expandable microspheres is not greater than40 degree.C. In other words, the hot gas flow just before or at thecontact with dispersed heat-expandable microspheres has a temperaturedistribution only within 40 degree.C. The temperature difference (ortemperature distribution) should preferably be within 30 degree.C., morepreferably within 20 degree.C., further preferably within 10 degree.C.,and most preferably within 5 degree.C.

Here all of the above-mentioned points of temperature determinationshould locate almost on a plane vertical to the direction of the hot gasflow 8, and those points should preferably locate at an upstreamposition of the point where dispersed heat-expandable microspherescontact with the hot gas flow 8 for the first time, and at a downstreamposition of the turbulent flow generating member described below. Morepreferably the points for temperature determination should locate nearthe end of the hot gas nozzle, for example, the plane just above thearrow marked “X” in FIG. 1 (a). The number of the temperaturedetermination points is not specifically restricted, and shouldpreferably be at least 4, more preferably at least 6, and mostpreferably at least 8. Each of the temperature determination pointsshould preferably locate almost on a plane vertical to the direction ofthe hot gas flow 8 and almost on a circumference having its center at acertain point (preferably at the crossing point of the center line ofthe gas introducing tube and a plane vertical to the direction of thehot gas flow 8) in almost equal intervals with adjacent points.Specifically such points are represented by the four points A, B, C, andD shown in FIG. 1 (b) (located on the circumference in the order), whichalmost locate on a circumference having its center on the point O, andpreferably locate in almost equal intervals (intervals between A and B,B and C, C and D, and D and A) with adjacent points.

At the expansion step, the hot gas flow 8 may contain turbulent flowwhen it contacts to heat-expandable microspheres. In other words,turbulent flow may be generated in the hot gas flow with a turbulentflow generating member fixed at an upstream position of the hot gasflow. Such turbulent flow disturbs the stream of the hot gas flow 8, thetemperature of which varies depending on the regions of gas flowing, anddecrease the temperature difference of the hot gas flow at the contactto dispersed heat-expandable microspheres. The examples of the turbulentflow generating member include mesh 9 (refer to FIG. 2), a tray, and aring 10 (refer to FIG. 3.) The turbulent flow generating member shouldbe fixed to minimize the loss of gas flow pressure. For example, aturbulent flow generating member to be fixed to the hot gas flowsupplying pipe in FIG. 1 (a), which is curved and then straightened,should be positioned at the straightened zone as near as possible to thecurved zone (for example, near to the point marked 3).

The techniques for minimizing the temperature difference and forgenerating turbulent flow are not restricted within those mentionedabove, and other techniques may be employed. Examples of othertechniques include 1) mixing hot gas flow from plurality of hot gassources, not only one source, thereby to minimize the temperaturedifference due to the difference in gas flowing distance, 2) mixing thehot gas flow from plurality of hot gas sources described in 1) to swirlthe hot gas flow at the initial stage so as to minimize the temperaturedifference, and 3) making a space having a wider cross section than thatof the gas flow pass (for example, an expansion chamber 11 or the like,refer to FIG. 4) at an upstream position of the hot gas nozzle or anupstream position in the hot gas flow 8 as a turbulent flow generatingmember to minimize the temperature difference. In this case, the crosssectional area of the hot gas flow pass coming into the expansionchamber should preferably be wider than the cross sectional area of thehot gas flow pass going out of the expansion chamber as shown in FIG. 4.

In such manners, heat-expandable microspheres are thermally expanded andthen cooled down below the softening point of the thermoplastic resinshell with some means, such as passing them through a cooling zone, andresultant heat-expanded microspheres are collected. For collecting themicrospheres, ordinary solid-gas separators, such as cyclone separatorsor bag filters, may be employed.

In the production method of the present invention, both of heat-expandedmicrospheres having re-expanding temperature and not having re-expandingtemperature can be produced by controlling expanding conditions. Thecontrol of expanding conditions is not specifically restricted.

In the production method of the present invention, any of raw material,i.e., heat-expandable microspheres, can be subjected to almost the samethermal history owing to the high energy efficiency and easy temperaturecontrol, and the dispersibility of the heat-expandable microspheres ingas flow is improved. The heat-expanded microspheres obtained in themethod have high packing efficiency and high durability against repeatedcompression. In addition, the difference in the coefficient of variationin the particle size distribution of microspheres is minimized betweenbefore and after expansion, and the resultant heat-expanded microsphereshave uniform quality (particle size distribution and true specificgravity distribution, in particular). In other words, the heat-expandedmicrospheres obtained in the method contain minimum amount of aggregatedmicrospheres (excessively expanded microspheres) caused by excessiveheating or microspheres having high true specific gravity (raw materialmicrospheres or slightly expanded microspheres) caused by insufficientheating, and thus the variation of the bulk specific gravity of theheat-expanded microcapsules is minimized.

In this process, the expanding conditions are easily controlled asdescribed above, and thus almost completely heat-expanded microspheres,and heat-expanded microspheres which have a desirable re-expandingproperty can be produced.

[Heat-Expanded Microspheres]

The heat-expanded microspheres of the present invention are produced inthe production method where heat-expandable microspheres which comprisea shell of thermoplastic resin and a blowing agent having a boilingpoint not higher than the softening point of the thermoplastic resin andbeing encapsulated in the shell, and have an average particle sizeranging from 1 to 100 micrometer are heated at a temperature not lowerthan their expansion initiating temperature. The raw material,heat-expandable microspheres, are not specifically restricted, and theheat-expandable microspheres described above are preferable. Theproduction method for heating and expanding heat-expandable microspheresat a temperature not lower than their expansion initiating temperatureis not specifically restricted, and the process described above ispreferable.

The heat-expanded microcapsules of the present invention should have avoid fraction not higher than 0.70, preferably not higher than 0.65,more preferably not higher than 0.55, further preferably not higher than0.45, further more preferably not higher than 0.40, and most preferablynot higher than 0.35.

The void fraction is a physical property value for evaluating packingefficiency, and represents the ratio of void in the bulk volume ofheat-expanded microspheres. Therefore heat-expanded microspheres ofsmaller void fraction have higher packing efficiency, higher storage andtransportation efficiency, and good handling property.

The heat-expanded microspheres of the present invention should have arepeated-compression durability not lower than 75 percent, preferablynot lower than 78 percent, more preferably not lower than 80 percent,further more preferably not lower than 83 percent, and most preferablynot lower than 88 percent.

The repeated-compression durability is a physical property value forevaluating the durability of heat-expanded microspheres against mixingstress when they are mixed with other materials. The method ofevaluating the value is described in detail in Examples. Higher valuesof repeated-compression durability represent better durability ofmicrospheres against mixing stress.

Other materials are not specifically restricted, and the examplesthereof are rubbers, such as natural rubber, butyl rubber, and siliconerubber; thermosetting resins, such as epoxy resins and phenol resins;sealing materials, such as urethane and silicone polymers; paints ofvinyl chloride or acrylate compounds; inorganic materials, such ascement, mortar, and cordierite. These materials are mixed withheat-expanded microspheres to be made into hollow microspherecomposition.

The average particle size of heat-expanded microspheres may be freelydesigned according to their end uses, and is not specificallyrestricted. For attaining sufficient retention of encapsulated blowingagent and durability of heat-expanded microspheres, the average particlesize should preferably range from 1 to 1000 micrometer, more preferablyfrom 5 to 800 micrometer, and most preferably from 10 to 500 micrometer.

The coefficient of variation (CV) of the particle size distribution ofheat-expanded microspheres is not specifically restricted, and it shouldpreferably be not greater than 30 percent, more preferably not greaterthan 27 percent, and most preferably not greater than 25 percent.Heat-expanded microcapsules having a CV of 30 percent or more may havepoor durability against repeated compression.

For retaining the uniformity of particle size of heat-expandedmicrospheres, the difference between the CV of the particle sizedistribution of microspheres before and after expansion should be withinthe range of plus/minus 10 percent, preferably plus/minus 5 percent,more preferably plus/minus 3 percent, and most preferably plus/minus 1percent. The definition of the coefficient of variation, CV, isexplained with the expressions (1) and (2) in the above descriptionabout [Heat-Expandable Microspheres]. The difference in the coefficientof variation, CV, is defined as (CV of the particle size distribution ofheat-expanded microspheres obtained)−(CV of the particle sizedistribution of raw material, heat-expandable microspheres).

The ratio of aggregated microspheres contained in heat-expandedmicrospheres should be not greater than 5 weight percent for retainingthe uniformity of their true specific gravity, preferably not greaterthan 1 weight percent, more preferably not greater than 0.5 weightpercent, and most preferably not greater than 0.3 weight percent.Aggregated microspheres are detected by visual inspection throughelectron microscope, and their amount is determined by measuring theamount of microspheres remaining on sieve after screening heat-expandedmicrospheres.

The ratio of microspheres having a true specific gravity of 0.79 g/cc orhigher contained in heat-expanded microspheres at 25 degree.C.(hereinafter sometimes referred to as an abbreviation, “sedimentablecomponent ratio”) should be not greater than 5 weight percent forretaining the uniformity of the true specific gravity of heat-expandedmicrocapsules, preferably not greater than 3 weight percent, morepreferably not greater than 2 weight percent, and most preferably notgreater than 1 weight percent. The ratio of microspheres having a truespecific gravity of 0.79 g/cc or higher is determined by measuring theamount of sedimented component after the gravity separation of themicrospheres with isopropyl alcohol (having a specific gravity of 0.79at 25 degree.C.).

The expanding conditions in the above-mentioned production method may becontrolled to produce heat-expanded microcapsules having a re-expandingtemperature. The re-expanding temperature should be 90 degree.C. orhigher, preferably 100 degree.C. or higher, more preferably 110degree.C. or higher, and most preferably 120 degree.C. or higher.

The re-expanding ratio of the heat-expanded microcapsules having are-expanding temperature should be greater than 100 percent at theirmaximum expanding temperature, preferably not lower than 105 percent,more preferably not lower than 120 percent, further preferably not lowerthan 130 percent, and most preferably not lower than 150 percent.

The end uses of heat-expanded microspheres are not specificallyrestricted, and include a lightweight filler for automobile paints,expanding particulates in expandable inks for wallpaper and appareldesign, an expanding material for lightening resin compositions, asensitizer for explosives, a light diffuser, and a void-forming agent.

The present invention is described specifically with the followingexamples and comparative examples, though the present invention is notrestricted within the scope of those examples.

(Determination Methods and Definition)

[Determination of Average Particle Size and Particle Size Distribution]

A laser diffraction particle size analyzer (HEROS & RODOS, produced bySYMPATEC) was employed for the determination. Microspheres were analyzedin dry system with a dry dispersion unit, where the dispersion pressurewas controlled at 5.0 bar and the degree of vacuum was controlled at 5.0mbar. The D50 value was determined as an average particle size.

[Determination of True Specific Gravity]

The true specific gravity, ρp, of microspheres was determined with theliquid substitution method (Archimedean method) with isopropyl alcoholin an atmosphere at 25 degree.C. and 50% RH (relative humidity).

Specifically, an empty 100-cc measuring flask was dried and weighed(WB₁). Isopropyl alcohol was poured into the weighed measuring flaskaccurately to form meniscus, and the measuring flask filled withisopropyl alcohol was weighed (WB₂).

Then the 100-cc measuring flask was emptied, dried, and weighed (WS₁).About 50 cc of heat-expanded microspheres were filled into the weighedmeasuring flask, and the measuring flask filled with the heat-expandedmicrospheres was weighed (WS₂). Then isopropyl alcohol was poured intothe measuring flask filled with the heat-expanded microspheresaccurately to form meniscus without taking bubbles into the isopropylalcohol, and the flask filled with the microspheres and isopropylalcohol was weighed (WS₃). The values, WB₁, WB₂, WS₁, WS₂, and WS₃, wereintroduced into the following expression to calculate the true specificgravity (ρp) of the heat-expanded microspheres.

ρp={(WS ₂ −WS ₁)×(WB ₂ −WB ₁)/100}/{(WB ₂ −WB ₁)−(WS ₃ −WS ₂)}

[Determination of Ratio of Microspheres Having a True Specific Gravityof 0.79 g/cc or Higher at 25 degree.C. (Sedimentable Component Ratio)]

Heat-expanded microspheres were added to isopropyl alcohol having a truespecific gravity of 0.79 at 25 degree.C. to be subjected to gravityseparation, where microspheres are separated by the standard specificgravity, 0.79, into those floating on isopropyl alcohol being estimatedto have a true specific gravity lower than 0.79 g/cc, and thosesedimenting into isopropyl alcohol being estimated to have a truespecific gravity not lower than 0.79 g/cc. The microspheres sedimentedinto isopropyl alcohol were quantified to determine the ratio (weightpercent) of sedimentable component.

Specifically, 10 g of heat-expanded microspheres was packed in a 1-literseparation funnel, 700 cc of isopropyl alcohol was poured into theseparation funnel to be mixed for about 3 minutes, and then the funnelwas held motion less. Then each of the portions floating on andsedimenting in isopropyl alcohol was fractionated and taken up. Thesedimented portion was dried and weighed as Wd (g). The sedimentablecomponent ratio was calculated by the following expression.

Sedimentable component ratio(weight percent)=Wd/10×100

[Determination of Bulk Specific Gravity]

A stainless cup having 50 mm inside diameter and 100 cc unobstructedcapacity was weighed. (Wb) Then a tube for stopping powder flow wasfixed at the top of the stainless cup, and 200 cc of a sample(heat-expanded microcapsules) was filled in the cup. Then the sample inthe cup was tapped 180 times, and the tube was removed. The sample inthe cup was leveled at the top of the cup with a blade, and thestainless cup filled with the sample was weighed (Wa). The tapping wascarried out 180 times at a rate of 1 time/sec by lifting the cup 15 mmhigh. The bulk specific gravity, ρb (g/cc), was calculated by thefollowing expression.

ρb(g/cc)=(Wa−Wb)/100

[Packing Efficiency]

The packing efficiency was evaluated by the void fraction, e, calculatedby the following expression:

ε=1−ρb/ρp

where: ε is void fraction, ρb is the bulk specific gravity of a sample(heat-expanded microspheres) (g/cc), and ρp is the true specific gravityof a sample (heat-expanded microspheres) (g/cc).

[Determination of Moisture Content of Heat-Expandable Microspheres]

The moisture content was determined with a Karl Fischer moisture meter(MKA-510N, produced by Kyoto Electronics Manufacturing Co., Ltd.).

[Determination of Ratio of Blowing Agent Encapsulated in Heat-ExpandableMicrospheres]

1.0 g of heat-expandable microspheres was placed in a stainless steelevaporating dish 15 mm deep and 80 mm in diameter, and weighed (W₁).Then 30 ml of acetonitrile was added to disperse the microspheresuniformly. After being left for 30 minutes at room temperature, themicrospheres were dried at 120 degree.C. for 2 hours, and the dry weight(W₂) was determined. The ratio of encapsulated blowing agent wascalculated by the following expression.

Ratio of encapsulated blowing agent(weightpercent)=(W1−W2)(g)/1.0(g)×100−(moisture content)(weight percent)

(The moisture content in the expression was calculated as describedabove.)

[Retention]

The retention of an encapsulated blowing agent is the percentage of theratio of an encapsulated blowing agent after expansion (G₂) to the ratioof an encapsulated blowing agent before expansion (G₁), and calculatedby the following expression.

Retention(percent)=G ₂ /G ₁×100

[Determination of (Re-)Expansion Initiating Temperature and Maximum(Re-)Expanding Temperature]

Those properties were determined with DMA (DMA Q800, produced by TAInstruments). In an aluminum cup 4.8 mm deep and 6.0 mm in diameter, 0.5mg of heat-expandable microspheres (or heat-expanded microspheres) wereplaced, and an aluminum lid 0.1 mm thick and 5.6 mm in diameter wasplaced on the cup to prepare a sample. The sample was subjected to apressure of 0.01 N with a compression unit, and the height of the sample(H1) was measured. The sample was then heated in the temperature rangefrom 20 to 300 degree.C. elevating at a rate of 10 degree.C./min, beingsubjected to the pressure of 0.01 N with the compression unit, and thevertical change of the position of the compression unit was determined.The temperature at which the compression unit started to change itsposition to the positive direction was determined as a (re-)expansioninitiating temperature, and the temperature at which the compressionunit indicated the greatest change (H₂) was determined as the maximum(re-)expanding temperature. A (re-)expansion coefficient at the maximum(re-)expanding temperature, E, was calculated by the followingexpression.

E(percent)=H ₂ /H ₁×100

[Determination of Ratio of Aggregated Microspheres]

The existence of aggregated microspheres was identified visually throughelectron microscope.

At first, the average particle size, R, of heat-expanded microsphereswas determined. Then the ratio of aggregated microspheres contained inthe whole of the heat-expanded microspheres was calculated from theamount of aggregated microspheres remaining after screening theheat-expanded microspheres with a sieve of about 2.0 R opening, thetolerance of which is plus/minus 0.05 R. If a sieve of 2.0 R opening isnot available, the ratio of remaining microspheres after screening witha sieve of an opening within the range from 1.8 R to 2.0 R (except 2.0R) and the ratio of the remaining microspheres after screening with asieve of an opening within the range from 2.0 R to 2.2 R (except 2.0 R)may be proportionally distributed and calculated to determine an amountequal to the ratio of the microspheres to remain after screening with asieve of 2.0 R opening. For selecting each of sieves with an openingwithin the range from 1.8 R to 2.0 R (except 2.0 R) and from 2.0 R to2.2 R (except 2.0 R), a sieve having an opening as near to 2.0 R aspossible should be selected. The amount of a sample screened with asieve should be 1 liter or more.

[Determination of Repeated-Compression Durability]

In an aluminum cup 4.8 mm deep and 6 mm in diameter (having an insidediameter of 5.65 mm), 2.00 mg of heat-expanded microspheres were placed,and an aluminum lid 0.1 mm thick and 5.6 mm in diameter was placed onthe heat-expanded microspheres to prepare a sample. Then the sample wastested with DMA (DMA Q800, produced by TA Instruments), where the samplewas compressed on its aluminum lid with a compression unit at 25degree.C. being subjected to a pressure of 2.5 N, and the thickness ofthe layer of the heat-expanded hollow microspheres, L₁, was determined.Then the pressure was raised from 2.5 N to 18 N at a rate of 10 N/min,followed with the reduction of the pressure from 18 N to 2.5 N at a rateof 10 N/min. The pressure raising and reducing operation were repeated 7times, and the thickness of the layer of the heat-expanded hollowmicrospheres, L₂, was determined. Then the ratio between L₁ and L₂, thethickness of the layers of the heat-expanded hollow microspheres, wascalculated into repeated-compression durability by the followingexpression.

Repeated-compression durability(percent)=(L ₂ /L ₁)×100

Example 1

Heat-expanded microspheres were produced by heating and expandingMATSUMOTO MICROSPHERE F-100D (produced by Matsumoto Yushi-Seiyaku Co.,Ltd., comprising nitrile copolymer as thermoplastic resin shell, with anaverage particle size of 25 micrometer) with the manufacturing equipmentequipped with an expanding device (with a metal mesh of No. 30 mesh as aturbulent flow generating member) shown in FIG. 2. Before the dispersedheat-expandable microspheres contact to hot gas flow 8, the temperatureat each of the points in the hot gas flow 8 (which were eight pointslocating underneath the hot gas nozzle in almost similar distance fromthe nozzle and being arranged in almost similar distance from adjacentpoints) was determined, and the difference in the temperature (betweenthe highest and lowest temperature values) was 30 degree.C.

The expanding conditions were controlled into 0.10 kg/h for raw materialfeeding rate, 0.03 m³/min for the flow rate of gas containing dispersedraw material, 0.5 m³/min for the flow rate of hot gas, and 180 degree.C.for hot gas temperature. The property of the resultant expandedmicrospheres was determined and shown in Table 1.

Example 2

Heat-expanded microspheres were produced by heating and expanding themicrospheres in the same manner as in Example 1, except that themanufacturing equipment was replaced with an equipment equipped with theexpanding device (with a ring as a turbulent flow generating member)shown in FIG. 3. The difference in the temperature was 5 degree.C.

The property of the resultant expanded microspheres was determined andshown in Table 1.

Example 3

Heat-expanded microspheres were produced by heating and expanding themicrospheres in the same manner as in Example 1, except that themanufacturing equipment was replaced with an equipment equipped with theexpanding device (with an expansion chamber as a turbulent flowgenerating member) shown in FIG. 4. The difference in the temperaturewas 1 degree.C.

The property of the resultant expanded microspheres was determined andshown in Table 1.

Comparative Example 1

Heat-expanded microspheres were produced by heating and expanding themicrospheres in the same manner as in Example 1, except that themanufacturing equipment was replaced with an equipment equipped with theexpanding device (without turbulent flow generating member) shown inFIG. 1 (a). The difference in the temperature was 50 degree.C.

The property of the resultant expanded microspheres was determined andshown in Table 1.

Comparative Example 2

Heat-expanded microspheres were produced in the same manner as inExample 1 except that a circulation type dryer was used as amanufacturing equipment. Specifically, 100 g of MATSUMOTO MICROSPHEREF-100D was weighed, spread on detaching paper in an area about 100 cm²,and heated in an air circulation dryer at 180 degree.C. for 15 minutesto be processed into expanded microspheres.

The property of the resultant expanded microspheres was determined andshown in Table 1.

Example 4

MATSUMOTO MICROSPHERE F-100D, used in Example 1 and calcium stearate(AFCO CHEM CA-ST fine powder, with an average particle size of 2.0micrometer, supplied by Adeca Fine Chemical) were blended in 9:1 weightratio and uniformly mixed with a Super Mixer (manufactured by Kawata MFGCo., Ltd.) to produce heat-expandable microspheres coated with calciumstearate on their outer surface. The resultant heat-expandablemicrospheres were named as Trial product 1.

Heat-expanded microspheres were produced in the same manner as inExample 3 except that Trial product 1 was heated and expanded instead ofMATSUMOTO MICROSPHERE F-100D.

The property of the resultant expanded microspheres was determined andshown in Table 1.

TABLE 1 Comp. Comp. Example 1 Example 2 Example 3 example 1 example 2Example 4 Raw material MATSUMOTO MICROSPHERE F-100D Trial product 1Turbulent flow No. 30 metal Ring Expansion none — Expansion generatingmember mesh chamber chamber Temperature difference 30 5 1 50 — 1(degree. C.) Diagram or expansion FIG. 2 FIG. 3 FIG. 4 FIG. 1(a) — FIG.4 device Average particle size 96 95 95 97 96 95 (micrometer) Voidfraction 0.63 0.51 0.37 0.75 0.86 0.44 True specific gravity 0.028 0.0290.029 0.028 0.026 0.031 Repeated-compression 80 85 89 70 55 91durability (%) Ratio of sedimentable 0 0 0 0 0 0 portion (wt. %) Openingof sieve 1 175/0 175/0 175/0 175/0 175/27 175/0 (micrometer)/ratio ofaggregated microspheres (wt. %) Opening of sieve 2 210/0 210/0 210/0210/0 210/19 210/0 (micrometer)/ratio of aggregated microspheres (wt. %)

Example 5 Production of Trial Product 2

An aqueous phase was prepared by adding 150 g of sodium chloride, 3.0 gof an adipic acid-diethanolamine condensate, 20 g of colloidal silica(20-percent concentration), and 0.15 g of sodium nitrite to 500 g ofdeionized water, and by homogenizing the mixture with agitation.

An oily phase was prepared by mixing 180 g of acrylonitrile, 45 g ofmethacrylonitrile, 75 g of methacrylic acid, 1.2 g of trimethylolpropanetrimethacrylate, 2.0 g of azobisisobutyronitrile, and 150 g of C₃F₇OCH₃,and by agitating to dissolve the ingredients.

Then the aqueous phase and the oily phase were mixed preliminarily witha homogenizer at 3,000 rpm for 2 minutes, and then agitated at 10,000rpm for 2 minutes to prepare a suspension. Then, the suspension wastransferred into a reactor, purged with nitrogen, and polymerized at 61degree.C. for 20 hours with agitation. The polymerization product wasfiltered and dried. The resultant microspheres had an average particlesize of 25 micrometer, a CV or coefficient of variation of 24 percent,an expansion initiating temperature of 143 degree.C., and the maximumexpanding temperature of 205 degree.C.

The ratio of encapsulated blowing agent in Trial product 2 wasdetermined into 31.8 weight percent.

Trial product 2 was exposed to a source of ignition, but the product didnot burn.

(Heat-Expansion of Trial Product 2)

Then heat-expanded microspheres were produced by heating and expandingmicrospheres in the same manner as in Example 1, except that the rawmaterial heat-expandable microspheres, was the Trial product 2 mentionedabove and the hot gas temperature was settled at 240 degree.C. Beforethe dispersed heat-expandable microspheres contact to hot gas flow 8,the temperature at each of the points in the hot gas flow 8 almostlocating on a plane vertical to the direction of the hot gas flow 8 (theeight points which were located underneath the hot gas nozzle in almostthe same distance from the downstream position of the hot gas nozzle andin almost the same distance from adjacent points) was determined, andthe difference in the temperature (between the highest and lowesttemperature values) was 30 degree.C.

The property of the resultant expanded microspheres was determined andshown in Table 2.

Example 6

Heat-expanded microspheres were produced in the same manner as inExample 5, except that the manufacturing equipment was replaced with theequipment equipped with the expanding device (with a ring as a turbulentflow generating member) shown in FIG. 3. The difference in thetemperature was 5 degree.C.

The property of the resultant expanded microspheres was determined andshown in Table 2.

Example 7

Heat-expanded microspheres were produced in the same manner as inExample 5, except that the manufacturing equipment was replaced with theequipment equipped with the expanding device (with an expansion chamberas a turbulent flow generating member) shown in FIG. 4. The differencein the temperature was 1 degree.C.

The property of the resultant expanded microspheres was determined andshown in Table 2.

Comparative Example 3

Heat-expanded microspheres were produced in the same manner as inExample 5, except that the manufacturing equipment was replaced with theequipment equipped with the expanding device (with no turbulent flowgenerating member) shown in FIG. 1 (a). The difference in thetemperature was 50 degree.C.

The property of the resultant expanded microspheres was determined andshown in Table 2.

Example 8

The Trial product 2 and carbon black (KETJENBLACK ECP600JD, with anaverage particle size of 34 nm, supplied by Lion Corporation) wereblended in 9:1 weight ratio and uniformly mixed with a Super Mixer(manufactured by Kawata MFG Co., Ltd.) to produce heat-expandablemicrospheres coated with carbon black on their outer surface. Theresultant heat-expandable microspheres were named as Trial product 3.

Heat-expanded microspheres were produced by heating and expandingmicrospheres in the same manner as in Example 6, except that the Trialproduct 2 was replaced with the Trial product 3.

The property of the resultant expanded microspheres was determined andshown in Table 2.

TABLE 2 Comp. Example 5 Example 6 Example 7 example 3 Example 8 Rawmaterial Trial product 2 Trial product 3 Turbulent flow No. 30 metalRing Expansion none Ring generating member mesh chamber Temperaturedifference 30 5 1 50 5 (degree. C.) Diagram or expansion FIG. 2 FIG. 3FIG. 4 FIG. 1(a) FIG. 3 device Average particle size 86 85 85 86 84(micrometer) Void fraction 0.54 0.48 0.33 0.72 0.41 True specificgravity 0.031 0.032 0.032 0.031 0.036 Repeated-compression 76 81 85 6588 durability (%) Ratio of sedimentable 1.5 1.3 1.4 1.5 1.3 portion (wt.%) Opening of sieve 1 175/0 175/0 175/0 175/0 175/0 (micrometer)/ratioof aggregated microspheres (wt. %) Opening of sieve 2 — — — — —(micrometer)/ratio of aggregated microspheres (wt. %)

1. Heat-expanded microspheres having a void fraction not higher that0.70, and comprising a heated and expanded plurality of heat-expandablemicrospheres under a temperature not lower than their expansioninitiating temperature, the heat-expandable microspheres comprise priorto heating and expanding a shell of thermoplastic resin and a blowingagent encapsulated therein having a boiling point not higher than thesoftening point of the thermoplastic resin and has an average particlesize from 1 to 100 micrometer.
 2. Heat-expanded microspheres accordingto claim 1, which have a repeated-compression durability not lower than75 percent.
 3. Heat-expanded microspheres according to claim 1, whichcontain aggregated microspheres in an amount not higher than 5 weightpercent and contain microspheres having a true specific gravity notlower than 0.79 g/cc at 25 degree.C. in an amount not higher than 5weight percent.
 4. Heat-expanded microspheres according to claim 1,wherein the heat-expandable microspheres further comprise a particulatefiller adhering to the outer surface of the shell thereof, theparticulate filler having an average particle size not greater than onetenth of the average particle size of the heat-expandable microsphereswithout the particulate filler adhered to the surface thereof. 5.Heat-expanded microspheres according to claim 1, wherein the blowingagent contains a C₂₋₁₀ fluorine compound having an ether structure andcontaining no chlorine and bromine atoms.
 6. Heat-expanded microspheresaccording to claim 1, wherein the thermoplastic resin is produced bypolymerizing a monomer mixture consisting essentially of a nitritemonomer and the weight ratio of the nitrile monomer is not lower than 20weight percent of the monomer mixture.
 7. Heat-expanded microspheresaccording to claim 6, wherein the thermoplastic resin is produced bypolymerizing a monomer mixture consisting essentially of a nitrilemonomer and a monomer having a carboxyl group, the weight ratio of thenitrile monomer ranges from 20 to 80 weight percent of the monomermixture, and the weight ratio of the monomer having a carboxyl groupranges from 80 to 20 weight percent.
 8. A method of producingheat-expanded microspheres comprising the steps of: feeding a gas fluidcontaining a plurality of heat-expandable microspheres, eachheat-expandable microsphere comprising a shell of thermoplastic resinand a blowing agent encapsulated therein having a boiling point nothigher than the softening point of the thermoplastic resin, and theplurality of heat-expandable microspheres having an average particlesize from 1 to 100 micrometer, through a gas-introducing tube equippedwith a dispersion nozzle on an outlet thereof and fixed inside a hot gasflow, and then jetting the gas fluid from the dispersion nozzle; makingthe gas fluid collide with a collision plate fixed on a downstreamposition of the dispersion nozzle in order to disperse theheat-expandable microspheres in the hot gas flow; and bringing thedispersed heat-expandable microspheres into contact with the hot gasflow, the temperature difference of which does not exceed 40 degree.C.,and heating them at a temperature not lower than the expansioninitiating temperature of the heat-expandable microspheres and thusexpanding the same.
 9. A method of producing heat-expanded microspheresaccording to claim 8, wherein the hot gas flow contains turbulent flow.10. A method of producing heat-expanded microspheres according to claim9, wherein the turbulent flow is generated by a turbulent flowgenerating member set at an upstream position of the hot gas flow.
 11. Amethod of producing heat-expanded microspheres comprising the steps of:feeding a gas fluid containing a plurality of heat-expandablemicrospheres, each heat-expandable microsphere comprising a shell ofthermoplastic resin and a blowing agent encapsulated therein having aboiling point not higher than the softening point of the thermoplasticresin, and the plurality of heat-expandable microspheres having anaverage particle size from 1 to 100 micrometer, through agas-introducing tube equipped with a dispersion nozzle on an outletthereof and fixed inside a hot gas flow, and then jetting the gas fluidfrom the dispersion nozzle; making the gas fluid collide with acollision plate fixed on a downstream position of the dispersion nozzlein order to disperse the heat-expandable microspheres in the hot gasflow; and heating the dispersed heat-expandable microspheres in the hotgas flow, which contains turbulent flow generated by a turbulent flowgenerating member set at an upstream position of the hot gas flow, at atemperature not lower than the expansion initiating temperature of theheat-expandable microspheres and thus expanding the same.
 12. A methodof producing heat-expanded microspheres according to claim 8, whereinthe gas introducing tube and/or the collision plate has a function toprevent excessive heating.
 13. A method of producing heat-expandedmicrospheres according to claim 8, wherein the heat-expandablemicrospheres further comprises a particulate filler that adheres ontothe outer surface of the shell thereof, the particulate filler having anaverage particle size not greater than one tenth of the average particlesize of the plurality of heat-expandable microspheres without theparticulate filler adhered to the outer surface thereof.
 14. A method ofproducing heat-expanded microspheres according to claim 8, wherein theblowing agent contains a C₂₋₁₀ fluorine compound having an etherstructure and containing no chlorine and bromine atoms.
 15. A method ofproducing heat-expanded microspheres according to claim 8, wherein thethermoplastic resin is produced by polymerizing a monomer mixtureconsisting essentially of a nitrile monomer and the weight ratio of thenitrile monomer is not lower than 20 weight percent of the monomermixture.
 16. A method of producing heat-expanded microspheres accordingto claim 10, wherein the turbulent flow generating member is at leastone selected from the group consisting of mesh, trays, rings, andexpansion chambers.
 17. A method of producing heat-expanded microspheresaccording to claim 11, wherein the gas introducing tube and/or thecollision plate has a function to prevent excessive heating.
 18. Amethod of producing heat-expanded microspheres according to claim 11,wherein the heat-expandable microspheres further comprises a particulatefiller that adheres onto the outer surface of the shell thereof, theparticulate filler having an average particle size not greater than onetenth of the average particle size of the plurality of heat-expandablemicrospheres without the particulate filler adhered to the outer surfacethereof.
 19. A method of producing heat-expanded microspheres accordingto claim 11, wherein the blowing agent contains a C₂₋₁₀ fluorinecompound having an ether structure and containing no chlorine andbromine atoms.
 20. A method of producing heat-expanded microspheresaccording to claim 11, wherein the thermoplastic resin is produced bypolymerizing a monomer mixture consisting essentially of a nitrilemonomer and the weight ratio of the nitrile monomer is not lower than 20weight percent of the monomer mixture.
 21. A method of producingheat-expanded microspheres according to claim 11, wherein the turbulentflow generating member is at least one selected from the groupconsisting of mesh, trays, rings, and expansion chambers.